1. Field of the Invention
The present invention relates to the field of sealing piping passing through wall apertures and particularly to flexible seals for underground piping in access sumps at the interface between the pipe and the sump wall.
2.Problem to be Solved
Access sumps, which have openings called "manways", are used for easy access to pumps and underground plumbing components while also acting as containment chambers for any leaks or spills that may occur in the piping system. Spill containment has become an important consideration, for environmental reasons, when dealing with toxic chemicals or the handling of fuels in gasoline stations. Proper containment demands new standards for sealing the pipes and plumbing that enter or leave the containment sumps through wall apertures, that is, the pass- or feed-throughs must have some form of dependable and adaptable seals.
As a particular instance, below ground sumps have been used in the plumbing of gasoline stations for decades for both easy access to the critical pumps and fittings and, more recently, for the containment of small spills that could leach into the ground and cause pollution of drinking water in nearby buildings and homes. One of the paramount problems encountered in properly installing sump containment systems is the adverse environmental conditions that may exist at the installation site. These conditions may include everything from bad weather to dirt and water contamination during assembly. Such adverse conditions can make the precision alignment of pipes and fittings difficult, and, as a result, the piping may be offset or enter the sump at an angle. If the seals to the sump walls are made by welding (either steel or plastic), or by other rigid means, there may be delayed cracking of the joints because of long-term settling of components in the ground fill that can change the angle of the piping in the region where it enters the welded seal.
One of the most common problems during on-site installation of the sumps is the difficulty in cutting accurate holes in the sump wall, which, when out-of-round, can prevent proper sealing of the feed-through bushings. Consequently, initial seals are often subject to breakdown after the installation. Further, some of the presently used seals utilize hold-down bolts and inserts that are corrodible and require an accurate pattern of mounting holes. Drilling of these holes requires skill and frequently must be carried out under poor installation conditions.
Sumps are presently being made primarily of plastic, such as heavy walled polyethylene, to overcome the long term problem of the rusting out of metallic sump apertures. On-site plastic welding to make a seal between the piping and the interface bushings utilizes plastic rods that are melted around the feed-through bushing. This method when used to produce a long-term seal has had a high incidence of failure due to cracking by the weld. The most common causes of cracking at the welds involve: (1) the difficulty in making a good weld in cold weather; (2) the difficulty in maintaining clean surfaces during the welding process; and, (3) the fact that the newer cross-linked (rigid) polyethylene, which is approximately 100% stronger, cannot be used in the welding process thereby limiting the choice of best materials for overall long term durability of the sumps.
The commonly used solid fittings for the sump wall interface and pipe feed-throughs have proven to be a weak point due to the fact that when some of the underground components, such as the fuel tank, begin to settle or rise over a period of time the angle of the delivery pipes is caused to change thus setting up continuous stress on the less flexible seals.